This invention relates to the repair of alloy articles, and more particularly, to brazing alloy compositions used in an activated diffusion healing process utilized to repair gas turbine nozzles with service-induced damage.
There are numerous cobalt based alloys used in both the manufacture and repair of high-temperature operating gas turbine engine components including combustors, turbine vanes, nozzles, etc.
Representative examples of cobalt base alloys for the production and/or repair of superalloy articles are disclosed in U.S. Patent Nos. 4,830,934; 4,614,296; 4,381,944; 4,285,459; 4,058,415; 3,355,287; 3,276,865; 3,271,140; and 4,396,577.
During operation of such components under high-temperature operating conditions, various types of damage or deterioration can occur. For example, cracks can result from thermal cycling, foreign object impact, and/or corrosion. It is, of course, well known that the cost of these components is relatively high and therefore, it is more desirable to repair such components than to replace them.
The present invention relates to an improved brazing alloy composition for the repair of environmentally-damaged gas turbine parts exposed for long periods of time to corrosive high-temperature operation These brazing alloy compositions are specifically adapted for use in an activated diffusion healing process to rebuild, for example, nozzles, by brazing a mixture of the brazing alloy and the base metal of the nozzle in particulate form. Specifically, repair is affected by brazing a deposit containing a mixture of braze alloy and parent alloy powders. The vacuum brazing cycle causes the braze alloy to melt and alloy with the parent alloy powder and the parent substrate surface. A post-braze diffusion heat treatment cycle is then applied to promote further interdiffusion. The mechanical properties of the resultant repaired region nearly approach those of the parent alloy.
The brazing alloys in accordance with this invention are cobalt-base alloys with a high chrome content and also containing B and Si as melting point depressants. The latter are necessary to allow the brazing alloy to melt without also melting the parent alloy component.
The cobalt base alloys of this invention also emphasize the major MC-forming elements Ta and Hf.
Accordingly, in one preferred embodiment of this invention, a brazing alloy is provided which comprises, by weight:
______________________________________ Nickel from about 8.5% to about 12.5% Chromium from about 24% to about 40% Tungsten from about 0% to about 9% Carbon from about 0.03% to about 0.6% Boron from about 0.01% to about 3.5% Silicon from about 0.1% to about 11% Manganese up to about 2% Hafnium from about 0.1% to about 3% Tantalum from about 0.1% to about 8% Zirconium from about 0% to about 1% Titanium from 0% to about 1% Cobalt Balance ______________________________________
The alloys of this invention are high temperature (1200.degree.-1900.degree. F.) resistant and provide superior mechanical properties as well as oxidation and corrosion resistance in the above temperature range.
Other objects and advantages of the invention will become apparent from the detailed description which follows.